Many drugs are capable of penetrating the skin and getting into the general circulation system where they act systemically. Drugs which can be given in low doses and whose penetration is so great that the rate of invasion into the general circulation system can be controlled over the rate at which the active substance is released from the preparation, can be administered over longer periods of time more reliably and more accurately by means of a transdermal form of administration than, for example, per os. The advantages of the introduction of drugs into the general circulation system through the skin are the elimination of uncontrollable factors of gastrointestinal resorption, the reduction of the metabolism by avoiding the first liver passage, and the effects which are generally desired in retard forms, such as avoidance of high initial blood level concentrations and attainment of a constant blood level over a long period of time.
Various transdermal release systems for systemic drugs are known. U.S. Pat. Nos. 3,598,122, 3,598,123, 3,742,951, 3,787,494, 3,998,934, 3,995,632, 4,060,084, 3,731,683, and 4,031,894 describe sandwich-type or laminar bandages and adhesive plasters which consists of a supporting frame forming one surface of the bandage, a reservoir containing the systemic drug in solid suspended form, means applied on the surface of the reservoir for regulating the rate of release, as well as means for fastening the bandage or plaster on the skin. In addition, substrates in foil form with incorporated active substances are known from German Published Applications (DE-OS) Nos. 24 32 925, 22 18 200, and 22 07 635, which substrates consist of hydroxyalkyl cellulose, polyamino acids, or the like. Due to their complicated structure, the multi-layered systems are difficult to produce and require high investment and manufacturing costs. In addition, the effective substance contained in suspended form in multi-layered systems is only utilized to a limited extend, which corresponds to a low bio-availability. The other polymeric substrates consist of substances which are soluble in water and are therefore not suitable for dermal long-term application.